In general, mascara brushes have remained fundamentally similar to the twisted wire arrangements disclosed at least as early as 1964 in, for example, U.S. Pat. No. 3,214,782. In a typical twisted wire arrangement, a plurality of individual bristles are retained between metal wires that are twisted together to form a helical core. The bristles are clamped between the wires and are flared radially outward from the core to yield a brush with a substantially round cross-section. A handle, which can comprise, or be affixed to, a cap enables a user to dip the brush into a reservoir to remove and retain a volume of the liquid or pasty material and then to apply the material by combing the brush through the user's eyelashes.
Although they have varied in the shape and material composition of the bristles, wires, and the resulting contouring of the brush, twisted wire constructions are limited in their adaptability to different materials and application goals. The bristles in a twisted wire configuration necessarily tend to follow the helical pattern of the twisted wire core, and precise control over the location and orientation of the bristles is substantially impossible. Furthermore, mascara is trapped in the gaps between the bristles thereby reducing the crispness of the application process and establishing a haven for the accumulation of debris and other impurities leading to an undesirable result know as clumping of the product. Still further, the creation of a twisted wire arrangement is an inherently complex process having complicated processing and machinery requirements. Therefore, despite attempts to modify the character of the bristles, such as with very soft bristles as taught in PCT Application No. PCT/US01/04555 and with bristles having complex cross sections as in U.S. Pat. No. 7,051,740, the essential limitations imposed by the twisted wire configuration remain.
It will also be recognized that, since mascara is typically highly viscous, it can accumulate and clump when applied to eyelashes. Clumps and excessive accumulations are normally combed out and the lashes are ideally separated in a finishing step to the application process. Stiffer bristles disposed in a pattern with wide clearances between them allow the brush to comb out clumps and properly separate lashes. Conversely, soft bristles are considered well suited to the initial application of the mascara. Accordingly, while a separate brush could be used for each function, there is a recognized and longfelt need for a single brush that is simultaneously effective in applying mascara and in combing out clumps.
A number of inventors have sought to provide a brush that meets these very different goals. For example, U.S. Pat. No. 4,861,179 teaches a brush with a combination of soft and stiff bristles, and U.S. Pat. No. 5,238,011 discloses a brush with soft yet thick bristles designed to exhibit desirable softness while avoiding being excessively supple. Unfortunately, while the resulting brushes may have had some effectiveness when initially developed, increases in viscosity and other modifications to mascara compositions have rendered such designs less than ideal. For example, their soft bristles can collapse when confronted with modern high viscosity mascara.
More recently, applicator brushes have been developed where bristle projections are molded onto a rod-shaped support. For example, in U.S. Pat. No. 6,616,366, Weihrauch described an applicator where projections that are tapered toward the distal ends thereof are fixed in relation to a rod-shaped support. The projections and the rod-shaped support can be formed as a single part from a soft elastomer. Unfortunately, while the soft elastomeric material may be preferable for the projecting bristles, forming the support from that same material can yield a brush that is excessively flexible such that it can bend and wobble during use thereby harming the application process.
Weihrauch does contemplate molding a reinforcing insert into the support and bristle fingers, but the components are inherently fixed to one another and are fixed in their relative configurations. With this, any versatility in the resulting cross sectional or longitudinal profile of the applicator is prevented. Likewise, in U.S. Pat. No. 7,325,550, Eckers et al. disclose an applicator wherein a sleeve with radially projecting, round, tapered fingers is molded over a reinforcing core. As a result, the sleeve and the core are fixed in relation to one another such that the resulting cross section and longitudinal profiles of the sleeve are unchangeable. Moreover, with disparate materials fixed to one another, a dimensional change in one component in Weihrauch or Eckers et al., such as swelling of the soft bristle material due to prolonged exposure to somewhat harsh mascara products, can cause the sleeve and the core to separate leading to poor product performance and potential danger to the user.
Furthermore, where a sleeve is to be molded directly onto such a reinforcing core, the manufacturer is inherently limited in the cross-sectional and longitudinal profiles that can be achieved. In addition to being limited to the one chosen shape, the possibilities in shape are in and of themselves inherently limited since the tooling used to produce such brush sleeves is highly complicated, particularly since the molded bristles protrude in several directions. To accommodate the molding of the bristles, the molding tool must be designed to open in multiple directions thereby imposing substantial design limitations. Adding a varied cross section or a curved or other profile to the already complex bristle molding process would push the design out of the realm of commercial reasonableness or even beyond what is possible in the primary production tool.
In light of the state of the art as summarized above, it will be appreciated that there is a need in the art for a stable yet versatile applicator for mascara and a method for manufacturing the same with varied cross-sectional and longitudinal configurations that can enable an ample volume of material to be retained while providing smooth and consistent product payoff and effective combing and separation of eyelashes.